1. Field of the Invention
The present invention relates to a current lead unit and a superconducting magnet apparatus employing the same, and more particularly, to a demountable current lead unit and a superconducting magnet apparatus employing the same.
2. Description of the Related Art
A magnetic resonance imaging (MRI) apparatus includes a superconducting magnet. When the MRI apparatus is in charging operation mode, a current is transmitted from a power source at an ambient temperature, via current leads, to the superconducting magnet at an ultralow temperature of 4.2K maintained by cryogenic coolant. Since the superconducting magnet is usually operated with such a very high current (500 A is typical for an MRI apparatus), the current leads often serve as a significant heat source that transfers heat to the cryogenic coolant.
Traditionally, cryogenic losses in the current leads are addressed by cooling the current leads in a flow of helium gas boiled off from a liquid helium supply used to cool the superconducting magnet. Also, in the MRI apparatus, the cryogenic losses in the current leads may be reduced by disassembling the current lead part.
Meanwhile, even when the MRI apparatus is set in persistent operation mode, a current circulating in the superconducting magnet decays at a very slow exponential rate, and thus, it is necessary to increase the current to a predetermined maximum level at intervals. Since the current leads are cooled by liquid helium from a helium supply for cooling the superconducting magnet, a process for resupplying the current may also involve refilling the MRI apparatus with liquid helium. However, the process for refilling the liquid helium is costly and relatively complex.